1. Field of the Invention
The present invention relates generally to a returnless fuel system for a marine propulsion device and, more particularly, to a fuel system that regulates fuel pressure within a fuel rail and controls the speed of a fuel pump motor in order to maintain a desired pressure within the fuel rail.
2. Description of the Related Art
U.S. Pat. No. 5,673,670, which issued to Powell et al. on Oct. 7, 1997, describes a returnless fuel delivery system. A series-pass fuel pressure regulator in the system provides fuel of a regulated pressure to a fuel rail comprising at least one fuel injector. A bypass fuel pressure regulator provides fuel with a regulated pressure to the series-pass regulator. An in-line fuel filter is located downstream from the bypass regulator, such that only the fuel which reaches the series-pass regulator is filtered. A check valve is located downstream from the bypass regulator as well, to prevent fuel pressure bleed-down through the fuel pump and bypass regulator. A pressure relief valve is coupled to allow fuel with a pressure above a predetermined value to flow around the check valve.
U.S. Pat. No. 5,752,490, which issued to Rodgers et al. on May 19, 1998, describes a returnless fuel injection system for use with an internal combustion engine. The fuel system has a fuel pump, a throttle position sensor for sensing the power requested, and an engine control unit. The improvement comprises a fuel pump control circuit using three distinct duty cycle modulator circuits to control fuel pump speed.
U.S. Pat. No. 5,927,253, which issued to Oyafuso et al. on Jul. 27, 1999, describes a fuel system priming method. The method is intended for use with a returnless fuel system and electronic fuel injection. It includes the steps of sensing fuel pressure rate of rise during priming. A fuel pump is first activated to pressurize the system and then the injectors are controlled for a short interval in response to the sensed rate of pressure rise to vent trapped air in the fuel system.
U.S. Pat. No. 5,997,262, which issued to Finkbeiner et al. on Dec. 7, 1999, describes screw pins for a gear rotor fuel pump assembly. An in-tank type of electric motor fuel pump with a fuel inlet end cap, a fuel outlet cap, a case coaxially joining the end caps to form a pump housing, an electric motor mounted in the housing having a stator with spring-retained permanent field magnets surrounding the motor armature, and a gerotor pump in the housing rotatably driven by the motor armature is described.
U.S. Pat. No. 6,095,763, which issued to Bodzak et al. on Aug. 1, 2000, describes a fuel delivery pump with a bypass valve for a fuel injection pump for an internal combustion engine. The pump system includes a pair of gears that mesh with each other and are driven to rotate in a pump chamber. The gears deliver fuel from an intake chamber connected to a storage tank, along a supply conduit that is formed between the end face of the gears and circumference wall of the pump chamber, into a pressure chamber connected to the fuel injection pump. A conduit is integrated into a housing of the fuel delivery pump and connects the intake chamber to the pressure chamber. The conduit can be opened by means of a pressure valve disposed in it, wherein the pressure valve is functionally connected to a throttle valve that throttles the fuel supply into the intake chamber as a function of the controlled pressure on the control valve via the pressure chamber.
U.S. Pat. No. 6,099,263, which issued to Bodzak et al. on Aug. 8, 2000, describes a fuel delivery pump with a bypass valve and an inlet check valve for a fuel injection pump for internal combustion engines. The pump has a pair of rotating displacing elements which deliver fuel from an intake chamber connected to a storage tank along a supply conduit that is formed between the end face of the rotating displacing elements and the circumference wall of the pump chamber into a pressure chamber connected to the fuel injection pump and with a bypass conduit which is integrated into a housing of the fuel delivery pump and connects the intake chamber to the pressure chamber and which is opened by means of a pressure valve disposed in it, wherein the intake chamber is closed with a check valve that operates counter to the fuel delivery direction.
U.S. Pat. No. 6,296,458, which issued to Zacher et al. on Oct. 2, 2001, describes an electric fuel pump. The pump is intended for use with an internal combustion engine in which a pump mechanism is provided in a housing for pumping fuel from an inlet to an outlet of the housing. A DC motor in the housing is drivingly connected to the pump mechanism, the fuel flowing through is the housing past the motor to the outlet. A module including a commutation circuit for the DC motor is sealed in the housing from the fuel which flows therearound and cools the module.
U.S. Pat. No. 6,318,344, which issued to Lucier et al. on Nov. 20, 2001, describes a deadheaded fuel delivery system using a single fuel pump. The fuel pump draws fuel from a fuel tank via a fuel supply network or a fuel supply line, transfers the fuel through a fuel connector and a fuel filter, and delivers the fuel to a vapor separator.
U.S. Pat. No. 6,553,974, which issued to Wickman et al. on Apr. 29, 2003, discloses an engine fuel system with a fuel vapor separator and a fuel vapor vent canister. The system provides an additional fuel chamber, associated with a fuel vapor separator, that receives fuel vapor from a vent of the fuel vapor separator. In order to prevent the flow of liquid fuel into and out of the additional fuel chamber, a valve is provided which is able to block the vent of the additional chamber.
U.S. Pat. No. 6,575,145, which issued to Takahashi on Jun. 10, 2003, describes a fuel supply system for a four-cycle outboard motor. The engine includes a fuel injection system that includes a fuel pump, a plurality of fuel injectors, and a vapor separator. The vapor separator is in communication with the fuel pump and at least one fuel return line. The separator includes a vent for removing vapors from the fuel. The vapor separator also includes a canister position within the vapor separator below the vent.
U.S. Pat. No. 6,694,955, which issued to Griffiths et al. on Feb. 24, 2004, discloses a marine engine with primary and secondary fuel reservoirs. The system comprises first and second fuel reservoirs connected in fluid communication with each other. The first fuel reservoir is a fuel vapor separator which has a vent conduit connected in fluid communication with a second fuel reservoir. Under normal conditions, fuel vapor flows from the fuel vapor separator and into the second fuel reservoir for eventual discharge to the atmosphere.
U.S. Pat. No. 6,925,990, which issued to Konopacki on Aug. 9, 2005, discloses a method for controlling fuel pressure for a fuel injected engine. A fuel pressure control system for a fuel injected engine measures the fuel pressure at an outlet of a fuel pump and controls the operating speed of the fuel pump as a function of the difference between a desired pressure and a measured pressure. Signals are provided to the fuel pump which are pulse width modulated signals that have a pulse width determined as a function of the desired pressure at the outlet of the pump. The desired pressure is determined as a function of air flow into the engine, a desired air/fuel ratio which, in turn, is a function of engine speed and the load on the engine, and a desired fuel rate which is determined as a function of the air/fuel ratio and the air flow into the engine. The desired fuel rate is then used to select a pressure at the outlet of the pump which will result in the desired fuel rate.
U.S. Pat. No. 6,971,374, which issued to Saito on Dec. 6, 2005, describes a fuel supply system for an outboard motor. A vapor separator venting system vents fuel vapor from a fuel vapor separator through a vapor relief valve. The vapor relief valve is located in a high position on the outboard motor to ensure that liquid fuel does not reach the vapor relief valve.
U.S. patent application Ser. No. 11/290,013, which was filed by Konopacki on Nov. 30, 2005, discloses a returnless fuel system module. A returnless fuel system module includes a fuel pump in a fuel pump cavity, a fuel pressure regulator in a fuel pressure regulator cavity, first and second transfer passages therebetween, and a heat exchanger integrally formed in the housing in thermally conductive relation with at least the bypass relief passage.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
A paper titled “Fuel Rail Pressure Relief”, written by Ross Pursifull for the SAE technical paper series, discusses various fuel systems. It describes a major source of engine-off evaporative hydrocarbon emissions as being a result of fuel injector leakage. Methods and devices to relieve fuel rail pressure after key-off, and thus reduce leakage, are described in this paper. Impact on fuel manifold repressurization is also discussed. The basic principles governing this behavior, such as fuel thermal expansion, fuel vapor pressure, and dissolve gases in liquid, are described. Data is shown in this paper relating to fuel pressure relief.
Returnless fuel systems typically recirculate fuel, when more fuel is pumped to a fuel rail than is needed by the injectors connected to the fuel rail, by allowing a certain percentage of the pumped fuel to recirculate from the outlet of a fuel pump back to an inlet of the fuel pump or to a fuel reservoir. This recirculation of fuel requires energy to be expended and raises the temperature of the fuel that is recirculated. It would therefore be significantly beneficial if a fuel system could be provided which accurately maintains a desired pressure in the fuel rail without having to recirculate significant quantities of liquid fuel after it has been pressurized by the operation of a fuel pump.